Detergent compositions normally contain surfactants which tend to produce foam when agitated in aqueous solution. For many applications, especially in automatic washing and dishwashing machines, excess foam production is a serious problem and with many effective surfactants it is necessary to add foam suppressing or controlling agents in order to achieve acceptable sudsing characteristics.
Unfortunately, it has been found that the addition of foam controlling agents can in itself create new problems. For example, monostearyl acid phosphate, which is one conventional controlling agent, is very effective and useful at low levels in product, but as the level of phosphate is increased to cope, for example, with increased surfactant, the material becomes incompletely soluble in the wash solution and precipitates out of solution onto utensil and machine surfaces leaving them coated with unsightly streaks and deposits.
Another type of foam controlling agent which has often been suggested is that based on silicones, especially polydimethylsiloxane. These materials are known to be very useful in industrial applications where the silicone is added directly to an aqueous solution containing a surfactant. However, they have not lived up to their promise when incorporated into detergent compositions; frequently, for example, they become inactivated in the presence of other detergent ingredients and require some type of special protection as disclosed, for instance, in U.S. Pat. No. 3,933,672. Also, in the case of granular compositions, addition of silicone foam-controllers can lead to problems of increased "wetting" of detergent substrate in an aqueous medium with the result that the product has poor dispensing characteristics in washing machines and leaves gel-like residues on the inside of the product dispenser. In addition, silicone foam-controllers can have a deleterious effect on the surface-feel of fabrics washed therein, and can also adversely affect the cleaning characteristics of detergent compositions.
One type of silicone-based foam-controller which requires no special protection to prevent inactivation in the presence of other detergent ingredients, is the so-called "self-emulsified" silicone class disclosed generally in British Pat. Nos. 1,533,610 and 1,544,736. The preferred self-emulsified foam-controller disclosed therein are those containing emulsifiers having at least one polyoxyalkylene moiety incorporated into a basic polysiloxane structure. Mixtures of these emulsifiers with polydimethylsiloxanes are also generally disclosed, the mixtures containing at least 50% of emulsifier and from about 5% to 45% of polydimethylsiloxane liquid.
Although the "self-emulsified" silicon foam-controllers disclosed above successfully overcome the inactivation problem in the presence of other detergent ingredients, they are still found to suffer a number of drawbacks which limit their commercial and practical value. In the first place, the "self-emulsified" silicones are found to be relatively inefficient foam-controllers, in other words, one requires a relatively high level of the foam regulating material for satisfactory performance. In addition, "self-emulsified" silicones are found to be relatively sensitive to the prevailing wash conditions (soil load, fabric/liquor ratio, wash temperature etc); in other words, "self-emulsified" silicones lack "robustness." Moreover, the "self-emulsified" silicones tend to have a flocculating effect on silica dispersions and this can lead to a loss of suds suppresion effectiveness after prolonged storage of the foam controller in a detergent composition.
The present invention thus provides a detergent composition having improved foam control characteristics, especially foam-controller efficiency, robustness and storage stability; it also provides a detergent composition having improved foam control without detriment to detergency performance or "feel" characteristics of fabrics washed therein: and it further provides a foam-controlled detergent composition having excellent dispensing characteristics in automatic washing machines.